Method of lacquering cathode ray tube panels

ABSTRACT

D R A W I N G THIS DISCLOSURE DEPICTS IMPROVED METHOD AND APPARATUS FOR AUTOMATICALLY PROCESSING FRONT PANELS OF CATHODE RAY TUBES IN A CONTINUOUS STEP-BY-STEP FASHION INCLUDING SPRAYING A LAQUER COATING ONTO A PHOSPHOR COATING ON THE PANELS. THE FRONT PANELS ARE LOADED IN A FRONT-SIDE-UP ATTITUDE ONTO AN ANNULAR ENDLESS CONVEYOR WHICH IS STEPPED AROUND A PLURALITY OF DISCRETE WORK STATIONS DISPOSED AROUND THE PERIMETER OF THE CONVEYOR, EACH OF THE WORK STATIONS BEING ADAPTED TO PERFORMED AT LEAST ONE PREDETERMINED OPERATION ON THE PANELS. LACQUER APPLICATOR MEANS IS SITUATED IN AT LEAST ONE SAID WORK STATIONS FOR APPLYING A LACQUER COATING ON THE PANELS. ENCLOSURE MEANS ARE PROVIDED FOR ENCLOSING THE LAQUER APPLICATOR AND ASSOCIATED DRYING STATIONS TO PREVENT ESCAPE OF LAQUER VAPORS TO THE ENVIRONMENT. VERTICALLY MOVABLE SHROUD MEANS ARE PROVIDED AT THE LAQUER APPLICATION STATION FOR ENSHROUDING THE PANELS DURING THE LAQUER APPLYING OPERATION TO MINIMIZE AIR CURRENTS WHICH MIGHT DISTURB THE SURFACE OF THE WET LACQUER.

METHOD OF LACQUERING CATHODE RAY TUBE PANELS Filed Dec. 29, 1972 Aug. 27, 1974 C.A. cooK ETAL 3 Sheets-Sheet 1 Aug. 27, 1974 c. A. COOK ETAL 3,832,211

METHOD OF LACQUERING CATHODE R AY TUBE PANELS Filed Dec. 29, 1972 3 Sheets-Shoot 2 FIG. 3

To Lacquer p y METHOD OF LAC UERING CATHODE RAY TUBE PANELS Filed Dec. 29, 1972' z- 7., 1974 c. A. COOK ETAL 3 Sheets-Sheet 5 A 0mm v H Z05 Q xwu P I am mom QL Eam Entmw m United States Patent Office 3,832,211 Patented I Aug. 2' 7, 1974 3,832,211 METHOD OF LACQUERING CATHODE RAY TUBE PANELS Charles A. Cook, Buffalo Grove, and Thaddeus J.

Hajduk, Chicago, 11]., assignors to Zenith Radio Corporation, Chicago, Ill. Filed Dec. 29, 1972, Ser. No. 319,970

Int. Cl. BOSc 11/10; B44d 1/08; C03c 17/10 US. Cl. 117-335 C 1 Cl ABSTRACT OF THE DISCLOSURE This disclosure depicts improved method and apparatus for automatically processing front panels of cathode ray tubes in a continuous step-by-step fashion including spraying a lacquer coating onto a phosphor coating on the panels. The front panels are loaded in a front-side-up ciated drying stations to prevent escape of lacquer vapors to the environment. Vertically movable shroud means are provided at the lacquer application station for enshrouding the panels during the lacquer applying operation to 'minimize air currents which might disturb the surface of the wet lacquer coating.

BACKGROUND OF THE INVENTION The present invention pertains to the manufacture of color cathode 'ray tubes of the shadow mask type presently in commercial use in color television receivers. It is specifically directed toward apparatus and method for processing and applying a lacquer coating to the phosphor coated side of the front panel-s of such tubes.

A picture tube can be thought of as consisting of two separate units, each manufactured and processed separately, which are united to form a completed picture tube.

I The first unit is the front panel assembly which consists 'of the glass front panel, the aperture (shadow) mask,

and the steel frame which supports and positions the shadow mask within the front panel.

The second unit consists of a funnel-shaped glass envelope containing the electron gun assembly in the neck I of the envelope. The manufacturing process of interest Therein applies only to the front panel unit; the discussion below will therefore be limited and directed toward that aspect of the manufacture of a color picture tube.

One part of the tube production operation involves depositing three superimposed layers of phosphor material. One well-known process for applying the phosphor layers is referred to as slurry screening. In practicing that process, a slurry coating of photosensitive resist and one of the three color phosphors is applied over the screen area of the front panel. After the coating has dried, it is exposed to actinic light which is directed through the shadow mask of the tube in process. As a consequence of this exposure, elemental areas of the slurry coating are rendered insoluble and the pattern thus formed is developedby washing the exposed screen with a solvent to remove the unexposed portions of the coating. The exposed insoluble areas which remain constitute the elements (the dots) of the. particular color associated with that slurry coating. This procedure is followed for each of the three colors with appropriate adjustment :in position of the exposing actinic light source for each phosphor, so that the color phosphor dots are properly arranged in triads.

Upon completion of the screening process, a thin lacquer coating is applied to the entire surface of the front panel. This lacquer coating serves to cover and fill in the area between the triad phosphor elements in order to provide a smooth surface for the application of a thin aluminum coating thereon. The aluminum coating serves, inter alia, to reflect light emitted by illuminated phosphor dots toward the front of the panel to effectively increase the brightness of a reproduced image as seen by a television viewer.

Before this invention, this lacquer coating operation has been a time consuming and inefficient partially manual operation having an unsatisfactory yield factor. Because of the volatile nature of the lacquer vapors which are generated during this step of the process, it has been found necessary to isolate the lacquer application apparatus from the apparatus associated with other steps of the tube manufacturing operation. In so doing, each panel has required substantial manual handling in transporting the panels to the isolated area. The need to isolate the lacquer applicating apparatus has until now created a bottleneck in the processing of cathode ray tube panel's.

As a result of this bottleneck in color cathode ray tube manufacturing operations and the relatively low yield factors from the lacquer applying operation, due to handling and nonuniform quality of the applied lacquer coatings, the cost of the end product tubes has been unnecessarily high. Further, prior art lacquer-applying processes require that manual operations be performed in the unpleasant lacquer environment.

OBJECTS OF THE INVENTION Accordingly, it is a general object of this invention to provide improved methods and apparatus for applying a lacquer coating to phosphor coatings on front panels of color cathode ray tubes.

It is a more specific object to provide improved apparatus and method for applying such lacquer coatings which is fully automated and which enables the lacquer-applying operation to be performed on a continuous basis and in line with other tube panel processing operations.

It is another object to provide improved lacquer-applying methods and apparatus which are faster than prior art methods and apparatus, which produces more uniform coatings, and which have substantially higher yield factors.

It is still another object to provide cathode ray tube lacquering methods and apparatus which do not require human contact with a vaporous lacquer environment.

BRIEF DESCRIPTION OF THE DRAWINGS The features of this invention which are believed to be new are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by reference to the following description in conjunction with the accompanying drawings in which like numbers refer to like elements and in which:

FIG. 1 is a side view, partially broken away, of cathode ray tube processing apparatus embodying the subject invention;

FIG. 2 is a sectional plan view, in part schematic, taken along the line 2-2 in FIG. 1, but with certain internal components removed to more clearly illustrate the invention;

FIG. 3 is an enlarged, partially sectional view of a portion of the FIG. 2 apparatus; and

FIG. 4 is a table indicating the timing of certain operations performed by the FIG. 2 apparatus. e

( .l p 7 3 DESCRIPTION OF THE PREFERRED EMBODIMENT .l

As briefly described above, the processes associated with the manufacture of cathode ray tube front panels includes depositing phosphor and photoresist materials in slurry form on the back side of the panels. The phosphor deposit is then exposed and developed in a manner well known in the art in order to generate a matrix of phosphor dots of one color in accordance with a predetermined dot pattern. The process of depositing the slurry on the front panel is known as screening. Apparatus for automatically performing such a screening process is depicted in US. Pat. No. 3,319,759, issued to T. J. Hajduk et al., assigned to the assignee of this invention. The apparatus described therein rapidly applies a uniform phosphor coating to the cathode ray tube panels with a minimum of manual handling. The panels are then screened, exposed and developed in the same manner for the other two phosphor colors to generate the well known red-bluegreen dot triad phosphor pattern.

The next step in the process is the application of a lacquer coating over the phosphors. This operation, in applicants knowledge, had never been implemented in a way which allowed the entire processing operation to proceed at'a satisfactory rate, at least not with any degree of uniformity in the finished panels. One requirement of the lacquer application process which tended to slow down the entire panel processing operation was the need to isolate the lacquer application apparatus from the rest of the panel processing machinery to insure that any lacquer vapors generated would be confined to a relatively small area in order to minimize the potential fire hazard. This need for isolation further aggravated the already relatively slow lacquer-application process by requiring that the phosphor coated panels be transported from the phosphor screening area to the lacquer application area.

Another aspect of panel processing which, until now, further slowed the production of cathode ray tubes was the necessity of first drying a panel which had been previously screened, exposed and developed with all three phosphor colors before the process of applying a lacquer coating could begin. Now, in accordance with this invention, because of the way in which the panel processing environment is controlled during the panel processing steps, a panel need not be first dried before receiving its lacquer coating. The elimination of the drying step permits each panel to be processed even faster. The steps taken to preserve a suitable environment for the speedier processing of the panels will be detailed in the discussion below.

In the description to follow, it will be shown how the adaptation of existing apparatus to the special requirements of the lacquer application process can result in a vastly improved method and apparatus for processing and applying the lacquer coating to a cathode ray tube panel.

Referring now to FIG. 1, there is shown, partly in schematic form, a side view of apparatus for processing color picture tube panels in accordance with the principles of this invention. As shown clearly in FIG. 2, the apparatus is generally circular. The apparatus comprises an endless annular conveyor which defines a circular processing path. Fifteen discrete work stations, labelled A-O, are equally spaced around the-perimeter of conveyor 10, at each of which at least one processing operation takes place. The processing steps which occurs at each work station will be detailed below after an overall description of the apparatus has been given.

Although the-preferred embodiment of the invention is shown in FIGS. 1 and 2 as being circular, it is contemplated that other embodiments thereof may have different shapes. An important aspect of this invention is that the panel processing operations take place in a continuous, closed loop-type fashion in order to provide a controlled atmosphere for the processing steps which are described below. The rotary-apparatus shown-"in 1 and 2 is well suited for such processing.

Attached to conveyor 10 are workpiece holders 12 which move with conveyor 10 from one work station to another in a step-by-step fashion. v

The step-by-step movementof conveyor 10 is" controlled by indexing means 13 which may bea conventional timer. Indexing means 13 is' shown in FIG. 1 as being mounted on the outer housing 20 of the apparatus, but it may also be situated at any convenient remote location.

Each workpiece holder12 is mechanically coupled to a rotatable panel support 14 which is adapted to. carry a picture tube panel 16 through each processing step. Note that every panel 16 is supported front side up so that its phosphor coated surface is directed downwardly toward the washing devices, lacquer application devices, etc. which are positioned beneath the panel positions at the several work stations.

Important advantages in processing the panels with their front sides up will be pointed out below WhCIl'La more detailed description of the lacquer application process is given.

Mounted on each workpiece holder 12 is a motor 18 coupled to each panel support 14 for spinning each panel support and its associated panel at predetermined speeds in order to facilitate the processing operations at each station. The speed of each motor is dependent-on the work station at which its supporting workpiece issituated. Switches (not shown in FIG. 2) are mounted on-brackets attached to conveyor 10 and situated'to come'intocontact with actuating cams (also not shown in FIG. 2) positioned at each work station. By varying the position of the cams at the several work stations, one OI'IIIOTErSC- lected speed control switches may be actuated to .-cause a motor 18 to run at a predetermined speed. The switches and cams will be discussed and pointed out in the description to follow. r

The components of the apparatus are confined within a housing 20 and supported by a base 22. Housing -20 is fitted with an enclosure 21 for enclosing work stations F-J which contain the lacquer application stations and associated drying stations. By enclosing those stations, volatile lacquer vapors which may bepresent are; prevented from escaping to th-IlVlfODlIl6IlL2 I In operation, a panel 16 is loaded at station A :Where there is preferably a loading. and-unloading.device 23 (not shown in detail) such as that described in copending application Ser. No. 327,916, filed'Jan. 3.0, 1973, assigned to the assignee of this invention. Upon a signal generated by indexing means 13, conveyor 10 movescounterclockwise until each workpiece holder is advanced-to the'next successive work station.

Prior to being loaded on this apparatus, each panel has received three phosphor coatings, the first two of which have been exposed and developed in a manner well known and practiced in the art. vThe last phosphor coating will have been exposed to actinic light forrendering insoluble its respective array of dots, stripes, or-in whatever geometric pattern the phosphor coatings are arranged. For purposes of this invention,'it is immaterial in what geometric pattern the phosphors are deposited. The panel is then loaded onto'the FIG. 2 apparatus. Upon advancement to station B, the last received phosphor coating is developed by rinsin'g'the downwardly facing phosphor coated surface with a suitable solvent to remove unexposed phosphor particles. A liquid caustic solution is then applied to the phosphorcoatedfsurface to further dissolve and remove unexposed phosphor particles. One advantage, of the process and apparatus according to this invention in which each panel is maintained in a front-side-up attitude is that any excessrinse water, solvents, dissolved particles or lacquer may more easily drop away from the panels. During the rinse, panel 16 is spun at a predetermined speed, preferably at about 7.5 r.p.m., in order to facilitate the developing process. f 'ilnirespon'seto 'a signal from indexing means 13, conveyor mam/ems panel 16 to work station C where the panel 16 further developed and washed. At this point, the panel remains'spinning at about 7.5 r.p.m.

Work station D includes apparatus for further rinsing each panel, scrubbing the outer skirt of each panel with brushes (not shown) and spraying a prewet solution onto the downwardly exposed surface of each panel. The prewet solution may be of any suitable type such as a water, polyvinyl alcohol, and potassium silicate combination which will provide a suitable liquid foundation for the subsequent application of a lacquer coating. At station D, thepanel continues to spin at about 7.5 r.p.m.

At station E, panel 16 is spun at about 65 r.p.m. to level off the prewet while receiving an air blast to facilitate drying. Stations F and G are also drying stations at which the P nel. 16 continues to spin at about 65 r.p.m.

" Work station H is the location at which each panel receives a lacquer coating. Details of the lacquer application assembly are shown in FIG. 3 and will be more thoroughly discussed below after a brief description of each of the 15 processing stations has been completed. After a panel 16 has been positioned at work station H, a shroud 26 having an open upper end is positioned around the panel 16. Positioned below panel 16 at work station H is a spray applicator assembly 28 which sprays the lacquer coating directly onto the downwardly exposed phosphor coated surface of the panel. Shroud 26 surrounds spray applicator 28 and when the panel above is ready to receive the lacquer spray, shroud 26 is vertically displaced so that it encloses, at least partially, both spray applicator 28 and panel '16. Thus enclosed within shroud 26, panel 16 is shielded from undesirable air currents during the lacquer application process which might otherwise cause unwanted disturbances on the lacquer coating. During the application of the lacquer spray, panel 16 is spun at 140 r.p.m. to insure a uniform distribution of lacquer. When the spray cycle is complete, shroud 26 is lowered away from panel 16.

At work stations I and I, each panel is spun at about 130 r.p.m. to level OE and make uniform the previously applied lacquer coating.

At station K, the rotational speed of each panel is reduced to about 7.5 r.p.m. This lower speed is continued at station L where there is applied a blast of hot air to assist the drying of the lacquer coating. At station M, spray nozzles (not shown) are situated beneath the panel in process for spraying a material on the underside of each panel elfective to eliminate the formation of blisters when the panel is heated and baked in subsequent processing. Hot air is then directed at the panel while it continues to spin at about 7.5 r.p.m.

Stations N and O are both drying stations at which the panels in process continue to spin at about 7.5 r.p.m. while they are dried by the application of hot air. The dried panel is then advanced to station A where it is unloaded.

The total processing time for each panel is about six minutes from loading to unloading. The table shown in FIG. 4 indicates how much time is allotted to each processing step at each of the 15 work stations. With only 24 seconds allocated to each work station, panels are processed at the rate of 150 per hour. This rate is a factor of 2 to 4 times greater than the speeds at which panels may be processed and lacquered by known prior art methods. An important advantage in practicing this invention is that the speed at which each panel is processed by the method and apparatus described herein is comparable with the speeds at which phosphor screening machines operate. The panels may be indexed from station to station at the same rate at which they are indexed from station to station in the three associated phosphor screening machines. The lacquer application apparatus described herein and the three phosphor screening machines may therefore all be indexed by a central timerfThis will enable" all four machines to proceed at the same speed and will reduce bottlenecks which result from one'proeessing step being substantially slower than the others.

Referring to FIG. 3, a more detailed description will be given of the apparatus andmethod used at station H to apply the lacquer coatingfjAs shown, panel :16 is in position to receive the lacquer coatingQ'By means of motor 30, gear reducer 32 and cam lifter34, shroud 26 and its supporting assembly 36 are driven upward to the elevated position as shown. Base 38 is vertically displaced until its lip 40 engages limit switch 42 which deactivates motor 30. Upon completion of the lacquer application cycle at station H, motor 30 lowers shroud 2-6 and its entire supporting assembly until lip 40 engages lower limit switch 44; switch 44 in turn deactivates motor 30. Excess lacquer drains from shroud 26 through drain 47 and is collected in a pan 49.

Note that panel support 14 includes overhanging members 46 which, along with the upward extending elements 48, enclose panel 16 within the housing 50 at station H. When panel support 14 is in its proper position at station H, elements 46 and 48 are positioned relative to one another as shown so as to partially seal and confine lacquer vapors within housing 50. Similar housings 50 are situated at stations F, G, I and J to further assist in the confinement of the lacquer vapors. Housings 50 and elements 46 also serve to preserve within their boundaries an atmosphere which is suitable for the processes at the several work stations. The sealing of the selected work stations is made easier because of the fact that the panels 16 remain in a front-side-up attitude throughout the entire processing operation. The same sealing method can then be used at each work station, if desired.

Panel support 14 also includes extending members 51 which, when shroud 26 is in its elevated position as shown in FIG. 3, assist in confining the lacquer and its vapor within shroud 26.

Spray applicator 28 preferably includes two spray nozzles 52 for applying a uniform lacquer coating to the panel. The lacquer is supplied to spray nozzles 52 via a flexible hose 54 which is connected to a source of lacquer (not shown).

Panel 16 and its support 14 are spun at about r.p.m. by means of motor 18 and connecting assembly 58. As mentioned briefly above, switches are mounted on each workpiece holder and situated so as to contact actuating cams positioned at each work station. These switches 60 and the earns 62 associated with work station H are schematically shown in FIG. 3. The cams 62 are positioned differently in each of the several work stations and serve as preprogrammed control means to cause each motor 18 to run at a predetermined speed at each work station.

Workpiece holder 12 also supports hanger '64. The mask frame assembly 66 associated with each front panel 16 hangs from hanger 64 as shown in FIG. 3. By keeping each mas-k frame assembly 66 with its panel 16 throughout the process, the chance of a mask being matched to the wrong panel is minimized.

Thus, it is apparent that there has been provided, in accordance with the invention, an improved color picture tube processing and lacquer application method and apparatus that fully satisfies the objects as set forth above. While the invention has been described in conjunction with specific embodiments. thereof, it is evident that many alterations, modifications and variations will be apparent to those skilled in the art in the light of the foregoing invention. Accordingly, it is intended to embrace all such alterations, modifications and variations which fall within the spirit and scope of the appended claim.

e whilesaid f rgnhside-upjpanel is spun at at least ope piprsli rm q dp edi.; s'pinfiing a d pa fla a r i siupmlpr posed to aIradiationVpattern, saidvmethod proyiding or 5 and; i r i the continuousl maintenance of. said panelilwith its drying said panel b'yl side 'up -and comprising; 4 to its' idownwardly facin 2. developing the phosphor layerv by rinsing said panel H q I with a solutionjto remove unexposed areas of pho sr Re'f eren'ic'es "Cited .phor par'ticle swhile said panel is supportedwith 1Q with dphototsr lve layer; ofv colored phosphors applied without having firstdr'ied the phosphor WILLIAM D. M ARTJN, r mary in-er spinning said panel with its front side up to provide a TRENOR, i 1 i uniform prewet foundation; I enclosing said front side-up panel within a shroud to V minimize undesirable air currents; r 20 117-435 CM, 96, 97, 101,1 spraying a lacquer coating over said prewet foundation r31392 R a; 

